Neural stimulation has been used to treat Peripheral Vascular Disease (PVD). It has been shown to restore tissue health by improving blood flow and reducing ischemia pain in peripheral limbs.
U.S. Pat. No. 6,058,331, incorporated herein by reference, describes a system including an implantable stimulation device for stimulating the spinal cord or a peripheral nerve. The system further includes an external sensor or limb sensor and an ischemia sensor that causes the stimulation to be delivered if the patient is experiencing an episode of ischemia.
Unfortunately, U.S. Pat. No. 6,058,331 and the prior art fail to provide relief in other important instances. These instances include any time the patient is active, any time the patient is at rest, or long term adjustment in the degree of stimulation based upon progression or regression of the patient's condition.
During physical exercise, and for those suffering from PVD, the blood in the peripheral limbs may be shunted. Instead, the blood is delivered to the actual large muscles performing the exercise. This results in claudication pain during exercise. Hence, it would be most beneficial to be able to provide stimulation whenever the patient is active.
With respect to pain when the patient is at rest, and particularly for end stage PVD, ischemia pain can become worse since gravity can no longer assist in promoting blood flow to the lower limbs. Hence, this calls for the ability to detect when the patient is at rest and provide stimulation at those times. This should significantly help any time the patient is lying down and resting for some length of time, such as when the patient is in the sleep state.
Lastly, the degree of stimulation should be controllable over long periods of time in keeping with the progression and regression of the patient's condition. This would require long term closed-loop evaluation and control so that if the patient's condition becomes worse, the degree of stimulation, whether the patient is active or at rest, is increased. Conversely, if the patient's condition improves over time, the degree of stimulation should decrease.
Activity would be a good measure of the progression or regression of PVD. As the condition becomes worse and the patient experiences more claudication and rest pain, the patient will become less active. Conversely, if the patient's PVD improves, the patient will become more active.
The present invention addresses these needs. It provides an implantable stimulation device capable of stimulating neural tissue whenever the patient is active or whenever the patient is at rest. It further provides long term closed-loop control of stimulation degree to fit the progression or regression of the PVD and hence the needs of the patient.